Hub structure for a rotary wing aircraft

ABSTRACT

A bearingless hub structure for a rotary-wing aircraft is provided, the structure including a hub body adapted to be securely connected to a rotor mast, a plurality of flexible beam members provided integrally with the hub body to extend radially outwardly, a pitch housing encircling each of the flexible beam members, and having a radially outward end portion which is rigid with a radially inward end portion of a rotor blade, a spherical bearing positioned adjacent to a radially inward end portion of the flexible beam member for supporting the pitch housing, a lead-lag damper positioned between the flexible beam member and the pitch housing, and the flexible beam members each having a flexible plate portion which is of a low bending rigidity in a flapping direction, a flexible portion provided radially outwardly of the flexible plate portion having a low bending rigidity in the lead-lag direction, and a twist-flex portion provided radially outwardly of the flexible portion. The flexible portion has two beam sections which have radially outward end portions integrally connected with a radially inward end portion of a twist-flex portion, with the radially inward end portions of the beam sections being removably connected to a radially outward end portion of the flexible plate portion at a plurality of circumferentially spaced positions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hub structure of a rotary-wingaircraft, and more particularly to a bearingless hub structure of arotary-wing aircraft.

2. Prior Art

A bearingless hub structure of a rotary-wing aircraft generally includesa hub body having a plurality of radially extending flexible beamsprovided with flexible plate sections having a low rigidity in theflapping direction. Each of the flexible plate sections is connected ormade continuous with a flexible portion which is flexible in thelead-lag direction. The flexible beam also has a twist-flex portionwhich is of a low torsional rigidity. As disclosed by the Japaneselaid-open patent application No. 61-21894 which has been laid-open topublic inspection on Jan. 30, 1986, the flexible plate section, theflexible portion and the twist-flex portion are formed in radiallyoffset positions with each other so that Coupling between the lead-lagmovements and the pitch changing movements can be eliminated. With thisarrangement, it is possible to obtain a design flexibility.

The U.S. Pat. No. 4,676,720 discloses a structure which is animprovement of the structure disclosed by the laid-open patentapplication No. 61-21894 to obtain an improved damping characteristics.More specifically, as described in the aforementioned U.S. patent, thestructure disclosed by the application 61-21894 has a tendency that theflexible beam is bent in an S-shaped configuration so that it isimpossible to provide a satisfactory damping property in the lead-lagdirection. As the result, it becomes difficult to prevent a instabilityon the ground and in the air.

In view of the problems, the U.S. patent proposes to provide theflexible portion which has a low rigidity in the lead-lag direction withtwo beam portions which are spaced apart at the radially inner ends inthe lead-lag direction and decreased in the spacing toward radiallyoutward direction. The beam portions are located radially inwardly withrespect to the twist-flex portion and has radially outward ends whichare continuously formed with the radially inner end of the twist-flexportion. The rotor blades are connected at the radially inner ends bymeans of a plurality of bolts to the radially outer end of the pitchhousing.

In rotary-wing aircrafts, it is necessary to fold the rotor blades whenthey are brought into hangers. For the purpose, in the aforementionedstructure, the bolts connecting each of the rotor blades to the pitchhousing are removed except one bolt about which the rotor blade isturned so that the rotor blade is placed along the longitudinal axis ofthe aircraft in a position wherein the rotor blade does not extendlaterally beyond the contour of the aircraft.

It should however be noted that in this structure the rigidity at theconnection between the rotor blade and the pitch housing will bedecreased in the lead-lag direction to an extent that a distortion maybe produced at this connection under a lead-lag movement. Suchdistortion may cause a decrease in the effective stroke of the lead-lagdamper so that there may be lack of damping capability. A furtherproblem encountered in this structure is that the connection between therotor blades and the pitch housing requires connecting bolts of asubstantial size and huge fittings so that the structure becomes bulkyand causes an increased aeronautical drag and weight. It should furtherbe noted that when the rotor blades are being folded as described above,there may be a possibility that the rotor blades may be accidentallydropped in handling. If such accident occurs, the twist-flex portion ofthe flexible beam section may be excessively twisted to an extent thatthe portion may be broken.

In order to eliminate the problem, the flexible beam may be separatedfrom the hub body at a portion radially inward of the flexible plateportion which has a low rigidity in the flapping direction and connectedwith the hub body through connecting bolts. This structure however hasdisadvantages. First, it should be noted that the portion radiallyinward the flexible plate portion. is subjected to a large bending loadin the flapping direction due to the flapping movements. The connectionat this portion therefore requires huge fittings which can withstand thebending load. Further, the connection provided in this portion willcause an interference between the rotor blades when the blades are to befolded.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a hubstructure of a rotary-wing aircraft in which the aforementioneddrawbacks are eliminated.

Another object of the present invention is to provide a bearingless hubstructure of a rotary-wing aircraft which can provide a sufficientstroke in the lead-lag damper.

A further object of the present invention is to provide bearingless hubstructure of a rotary-wing aircraft in which connecting structure can bemade compact.

Still further object of the present invention is to provide abearingless hub structure of a rotary-wing aircraft i which the bladesconnected with the hub structure can be conveniently folded.

According to the present invention, the above and other objects can beaccomplished by providing a hub structure with radially outwardlyextending flexible beam means including a flexible plate portion havinga low bending rigidity in a flapping direction, a flexible sectionprovided radially outwardly of the flexible plate portion and having alow bending rigidity in lead-lag direction, and a twistflex portionprovided radially outwardly of the flexible section and having a lowtorsional rigidity. The flexible portion includes two beam sectionshaving radially inward end portions spaced apart in the lead-lagdirection, the spacing between the beam sections being decreased towardradially outward. The radially outward ends of the beam sections areintegrally connected with a radially inward end of the twist-flexportion. The beam sections of the flexible portion are connected in aremovable manner at the radially inward ends with the radially outwardend of the flexible plate portion at least at two points by means ofvertically extending pins.

According to a preferable aspect of the present invention, damper meansmay be positioned between the two beam sections of the flexible portionand spherical bearing means may be provided in the damper means forconnecting a pitch housing to the hub structure. According to a furtheraspect of the present invention, the pitch housing may be provided at aposition corresponding to a space between the two beam sections withsupport means having pivot shaft means which is inserted into thespherical bearing means.

According to the present invention, it becomes possible to form a rotorblade integral with the pitch housing. Where advisable, the rotor blademay be formed separately from and connected to the pitch housing.However, the connection between the rotor blade and, the pitch housingmay not necessarily be removable. Therefore, the connection between therotor blade and the pitch housing does not cause any problem in respectof the rigidity in the lead-lag direction. Further, no huge fittingswill be required in the connection. The flexible beam means includes pinconnections between the radially inner end portion of the flexibleportion having a low rigidity in the lead-lag direction and the radiallyouter end portion of the flexible plate portion having a low rigidity inthe flapping direction. It is therefore possible to fold the rotor bladeby removing the connecting pins leaving one connecting pin so that therotor blade can be turned about the connecting pin which is left in theposition. The connection between the flexible portion and the flexibleplate portion is located radially inward with respect to the flexibleportion which produces a deflection in the lead-lag direction.Therefore, the rigidity of the connection does not have serious effecton the lead-lag deflection at the flexible portion. It is thereforepossible to provide a lead-lag damper with an adequate stroke bylocating the damper at or in the vicinity of the flexible portion. Bylocating the connection in the flexible beam means radially outward theflexible plate portion, it is possible to avoid mutual interferencebetween the rotor blades when the rotor blades are being folded.

According to the aforementioned preferable aspect of the presentinvention, the lead-lag damper means is located between the two beamsections of the flexible beam means and the spherical bearing means islocated in the lead-lag damper means for connecting the pitch housing tothe hub structure. In this structure, it is possible to house thelead-lag damper means in the space within the confine of the flexibleportion. This will make the entire structure compact. In the arrangementwherein the pitch housing is provided with the support means at aposition corresponding to the space between the two beam sections andthe support means is provided with pivot shaft means which is insertedinto the spherical bearing means for connecting the pitch housing withthe spherical bearing means, it is possible to make the overallstructure compact and light in weight. The connection between theflexible portion and the flexible plate portion of the flexible beammeans allows a slight rotational displacement so that a part of thelead-lag displacement is absorbed by this rotational displacement. Thiswill serve to decrease the bending stress at the beam sections of theflexible portion. It is therefore possible to decrease the length of thebeam sections. The above and other objects and features of the presentinvention will become apparent from the following description of apreferred embodiment taking reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hub structure of a rotary-wingaircraft in accordance with the present invention;

FIG. 2 is an exploded perspective view of the hub structure shown inFIG. 1;

FIG. 3 is a plan view of an elastomeric damper which is used in the hubstructure of FIG. 1;

FIG. 4 is a sectional view taken along a line a--a in FIG. 3;

FIG. 5 is a plan view of the flexible portion showing the beam sectionsin deformed positions;

FIG. 6 is a diagram showing the bending moment distribution along therotor blade through the flexible plate portion; and,

FIG. 7 is a plan view showing the rotor blades in folded positions.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, particularly to FIG. 1, there is shown abearingless hub structure 100 which includes a rigid hub body 2 securedto the upper end of a rotatable shaft or mast 1. The hub body 2 isformed with four flexible beam members 4 which are circumferentiallyspaced apart from each other by an angle of 90°. Each of the flexiblebeam members 4 is formed integrally with the hub body 2 and includes aflexible plate portion 3 which is located at a radially inward portionof the flexible beam member 4. The flexible plate portion 3 is of a flatconfiguration and extends in substantially horizontal direction toprovide flapping movements. The flexible beam member 4 further includesa flexible portion 29 which is located radially outward the flexibleplate portion 3. The flexible portion 29 is constituted by a pair ofbeam sections 8a and 8b which are circumferentially spaced apart fromeach other. The circumferential spacing between the two beam sections 8aand 8b are decreased from the radially inward portion toward radiallyoutward to form a substantially triangular configuration. The flexibleportion 29 has the least rigidity in the lead-lag direction to providelead-lag movements. Radially outside the flexible portion 29, the-flexible beam member 4 is again expanded in width toward radiallyoutward to form a twist-flex portion 9. The twist-flex portion 9provides feathering movements.

The flexible portion 29 and the twist-flex portion 9 are formedintegrally with each other. The flexible portion 29 is connected at aconnecting portion 5 with the flexible plate portion 3 by means of pins6. It will therefore be understood that the flexible beam member can bedisassembled by removing the pins 6.

The connecting portion 5 includes as shown in FIGS. 2 through 4connecting lugs 15 formed on the radially outward end portion of theflexible plate portion 3 and connecting lugs 16 formed on the radiallyinward end portions of the beam sections 8a and 8b. The connecting lugs15 and 16 include a plurality of lug elements 15a-1, 15a-2, 15b-1,15b-2, 16a-1, 16a-2, 16a-3, 16b-1, 16b-2, and 16b-3. The lug elements15a-1 and 15a-2 are engaged with the lug elements 16a-1, 16a-2 and16a-3, whereas the lug elements 15b-1 and 15b-2 are engaged with the lugelements 16b-1, 16b-2 and 16b-3.

An elastomeric damper assembly 7 is disposed in the connecting portion 5for providing a damping action in the lead-lag direction. Theelastomeric damper 7 includes an upper support plate 18a, a lowersupport plate 18b and a plurality of intermediate plates 20. Sheets 19of elastomeric material are interposed between and adhered to the plates18a, 18b and 20. A support block 21 is interposed between theintermediate plates 20 with a sheet 21 of the elastomeric materialdisposed at each side of the support block 21. The support block 21supports a spherical bearing 17 which is provided in the block 17. Thesupport plates 18a and 18b are provided at the opposite end portionswith holes for receiving the pins 6. As shown in FIGS. 1 and 2, thedamper 7 is located in the space between the beam sections 8a and 8b.The upper plate 18a is located over the lug elements 16a-1 and 16b-1whereas the lower plate 18b is located beneath the lug elements 16a-3and 16 b-3 so that the holes in the plates 18a and 18b are axiallyaligned with the holes in the lug elements. The pins 6 are insertedthrough the holes in the plates 18a and 18b and the lug elements toconnect the flexible plate 3 to the beam sections 8a and 8b.

As shown in FIG. 4, the pin 6 is of a stepped configuration and has asmall diameter portion at the lower end. The small diameter portion isinserted into the hole of the lower plate 18b. It will therefore beunderstood that when a nut 30 is tightened onto the pin 6 the lowerplate 18b is firmly engaged with the step portion between the largediameter portion and the small diameter portion of the pin 6. In thisposition, the elastomeric material of the sheets 19 is subjected to acompression stress. The precompression thus applied to the elastomericmaterial is effective to prevent a decrease in the fatigue resistance ofthe material under a oscillating load. This structure is also effectiveto prevent the lug elements 15 and 16 from being subjected to verticalbending loads.

Loads on the spherical bearing 17 is transmitted from the support block21 through the elastomeric sheets 19 to the support plates 18a lad 18band then through the pins 6 to the flexible beam member 4. The sheets 19of the elastomeric material are interlaced between the plates 18a, 18band 20 so that it is rigid in the vertical or flapping direction andresilient in the rotational or lead-lag direction. The elastomericmaterial has a large damping property so that it can provide asubstantial damping characteristics against the lead-lag movements.

Referring now to FIGS. 1 and 2, it will be noted that a pitch housing 10is formed integrally with a rotor blade 12. The pitch housing 10 has aradially inward end portion which is provided at a circumferentiallyintermediate portion with a block member 13 which has a radiallyinwardly extending pivot shaft 14. The pivot shaft 14 is inserted into aradially extending bore formed in the spherical bearing 17 so that alead-lag movement of the rotor blade 12 is transmitted to theelastomeric damper 7.

The rotor blade 12 is connected with the flexible beam member 4 at theradially outward end portion of the member 4 by means of pins 11. Thus,centrifugal force produced in the rotor blade 12 is transmitted throughthe pins 11 to the flexible beam member 4. Referring to FIG. 5, it willbe noted that a lead-lag movement of the rotor blade 12 causes adeflection in the twist-flex portion 9 of the flexible beam member 4.The deflection of the portion 9 produces a translational displacement inthe lead-lag direction as shown by δ in FIG. 5 and an angulardisplacement θ₁. The beam sections 8a and 8b are bent as shown andsubjected to a tensile and compression stresses. Since the beam sections8a and 8b are formed of a composite material so that they have a greaterrigidity against the compression and the tension but have a lessrigidity against the bending deformation. With this property of thecomposite material, the flexible portion 29 provides the least rigidityagainst the rotational lead-lag displacement and greater rigidityagainst the translational lead-lag displacement.

Since the beam sections 8a and 8b are connected with the flexible plateportion 3 through the lug structure 16, a slight angular displacement isallowed in this connection. More specifically, when the twist-flexportion 9 produces the angular displacement θ₁, there is produced ineach of the connecting portions 16a and 16b an angular displacement θ₂.It will therefore be understood that the connection between the beamsections 8a and 8b and the flexible plate portion 3 provides anincreased angular lead-lag displacement as compared with an arrangementwherein the beam sections are rigidly connected with the flexible plateportion. The angular displacement θ₂ is also effective to decrease thebending stress to a substantial extent so that it becomes possible toshorten the beam sections 8a and 8b. As the result, the hub structurecan be made compact and light in weight.

In the specific structure wherein the rotor blade 12 is integral withthe pitch housing 10, the rigidity in the lead-lag direction can besubstantially increased as compared with a structure wherein theseportions are separately made and connected together by means offittings. It will therefore be understood that this specific structureof the present invention can provide a sufficient extent of dampingeffect with an elastomeric damper of a smaller size. In the prior artstructure, there has been problems in that deformations anddisplacements are produced in the twist-flex portion and the connectionbetween the rotor blade and the pitch housing and such deformation andthe deflections have caused a decrease in the lead-lag movements tothereby decrease the effective stroke of the lead-lag damper. Thestructure of the present invention is effective to eliminate orsubstantially decrease the problems.

As shown in FIG. 2, the block member 13 and the elastomeric damper 7 aredisposed in a space encircled by the beam members 8 and the lugs 16.With this arrangement, it is possible to obtain a compact and light hubstructure.

Referring to FIG. 6, there is shown a load distribution in the hubstructure. At the connection with the rotor mast 1, there is produced abending moment of the maximum value. Under a lift force which isproduced in the rotor blade 12, the rotor blade 12 is swung upward toproduce a flapping movement. The axis of the rotor blade 12 intersectsthe plane 24 of the hub structure which is perpendicular to the axis ofthe rotor mast 1 at a point 26. Thus, the rotor blade 12 in appearancemakes a flapping movement about the point 26 so that the point 26 may bereferred to as the equivalent flapping hinge. The bending momentdecreases from the center of the hub structure toward the equivalentflapping hinge 26 and then increase again toward radially outwards. Theequivalent flapping hinge 26 is located in a substantially centerportion of the flexible plate portion 3 so that the connecting lugstructure 5 is located in a position where the bending moment is thesmallest. Thus, it is possible to make the connecting lug structurecompact.

According to the hub structure of the present invention, the rotorblades 12 can be folded as shown in FIG. 7. In FIG. 7, diametricallyopposite two of the four rotor blades 12 are folded to extend along theremaining two. More specifically, in each of the rotor blades 12 whichare to be folded, one of the connecting pins 6 is removed and the blade12 is turned about the other connecting pin 6 for 90°. A blade clamp 22is provided to hold the rotor blade 12 in the folded position. Accordingto the structure of the present invention, it is possible to avoid thetwist-flex portion 9 being subjected to the weight of the rotor blade 12when the rotor blade 12 is being folded.

The invention has thus been shown and described with reference to aspecific embodiment, however, it should be noted that the invention isin no way limited to the details of the illustrated structures butchanges and modifications may be made without departing from the scopeof the appended claims.

We claim:
 1. A bearingless hub structure of a rotary wing aircraft including a hub body which is adapted to be connected with a rotor mast, a plurality of flexible beam members provided integrally with the hub body to extend radially outward, a pitch housing encircling each of said flexible beam members with a spacing therebetween, said pitch housing having a radially outward end portion which is rigid with a radially inward end portion of a rotor blade, spherical bearing means provided adjacent to a radially inward end portion of said flexible beam member for supporting a radially inward end portion of said pitch housing, lead-lag damper means provided between said flexible beam member and said pitch housing for providing a damping function in a lead-lag direction, the improvement comprising that said flexible beam member includes a flexible plate portion which is of a low bending rigidity in a flapping direction, a flexible portion provided radially outward said flexible plate portion and of a low bending rigidity in the lead-lag direction and a twist-flex portion provided radially outward said flexible portion, said flexible portion being consisted of two beam sections which have radially inward end portions spaced apart in the lead-lag direction with a spacing which decreases toward radially outward, said beam sections having radially outward end portions integrally connected with a radially inward end portion of said twist-flex portion, said radially inward end portions of said beam sections being formed with lug means removably connected through bolt means with correspondingly formed lug means in a radially outward end portion of said flexible plate portion oat a plurality of positions spaced apart in the lead-lag direction, said damper means including upper and lower elastomeric dampers attached respectively to upper and lower surface portions of said spherical bearing means, said upper elastomeric damper having a support plate attached to an upper surface portion of said upper elastomeric damper and extending in the lead-lag direction, said lower elastomeric damper having a support plate attached to a lower surface portion of said lower elastomeric damper and extending in the lead-lag direction, said support plates of said upper and lower elastomeric dampers being connected to said flexible beam member at said lug means through said bolt means, and said pitch housing being provided with support means having a radially inwardly extending pivot shaft which is inserted into said spherical bearing means.
 2. A hub structure in accordance with claim 1 in which said damper means is disposed in a space between said beam sections.
 3. A hub structure in accordance with claim 1 in which said damper means includes a plurality of plates with a sheet of elastomeric material interposed between each adjacent two of said plates.
 4. A hub structure in accordance with claim 3 in which said spherical bearing means is located between adjacent two of said plates of said damper means with a sheet of elastomeric material interposed between each one of said plates and said spherical bearing means. 